US20230243934A1 - Light source device and measurement apparatus - Google Patents

Light source device and measurement apparatus Download PDF

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Publication number
US20230243934A1
US20230243934A1 US17/993,821 US202217993821A US2023243934A1 US 20230243934 A1 US20230243934 A1 US 20230243934A1 US 202217993821 A US202217993821 A US 202217993821A US 2023243934 A1 US2023243934 A1 US 2023243934A1
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light
emitting
thyristor
source device
vcsel
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Seiji Ono
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Fujifilm Corp
Fujifilm Business Innovation Corp
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Fujifilm Corp
Fujifilm Business Innovation Corp
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    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03K—PULSE TECHNIQUE
    • H03K17/00—Electronic switching or gating, i.e. not by contact-making and –breaking
    • H03K17/51—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the components used
    • H03K17/56—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the components used by the use, as active elements, of semiconductor devices
    • H03K17/72—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the components used by the use, as active elements, of semiconductor devices having more than two PN junctions; having more than three electrodes; having more than one electrode connected to the same conductivity region
    • H03K17/73—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the components used by the use, as active elements, of semiconductor devices having more than two PN junctions; having more than three electrodes; having more than one electrode connected to the same conductivity region for dc voltages or currents
    • H03K17/732—Measures for enabling turn-off
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
    • G01S7/483—Details of pulse systems
    • G01S7/484—Transmitters
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B11/00—Measuring arrangements characterised by the use of optical techniques
    • G01B11/24—Measuring arrangements characterised by the use of optical techniques for measuring contours or curvatures
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
    • G01S17/88—Lidar systems specially adapted for specific applications
    • G01S17/89—Lidar systems specially adapted for specific applications for mapping or imaging
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
    • G01S7/481—Constructional features, e.g. arrangements of optical elements
    • G01S7/4814—Constructional features, e.g. arrangements of optical elements of transmitters alone
    • G01S7/4815—Constructional features, e.g. arrangements of optical elements of transmitters alone using multiple transmitters
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
    • G01S7/483—Details of pulse systems
    • G01S7/486—Receivers
    • G01S7/4865—Time delay measurement, e.g. time-of-flight measurement, time of arrival measurement or determining the exact position of a peak
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/02—Structural details or components not essential to laser action
    • H01S5/022—Mountings; Housings
    • H01S5/0225—Out-coupling of light
    • H01S5/02257—Out-coupling of light using windows, e.g. specially adapted for back-reflecting light to a detector inside the housing
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/04—Processes or apparatus for excitation, e.g. pumping, e.g. by electron beams
    • H01S5/042—Electrical excitation ; Circuits therefor
    • H01S5/0428—Electrical excitation ; Circuits therefor for applying pulses to the laser
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/40—Arrangement of two or more semiconductor lasers, not provided for in groups H01S5/02 - H01S5/30
    • H01S5/42—Arrays of surface emitting lasers
    • H01S5/423—Arrays of surface emitting lasers having a vertical cavity
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03K—PULSE TECHNIQUE
    • H03K17/00—Electronic switching or gating, i.e. not by contact-making and –breaking
    • H03K17/51—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the components used
    • H03K17/56—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the components used by the use, as active elements, of semiconductor devices
    • H03K17/72—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the components used by the use, as active elements, of semiconductor devices having more than two PN junctions; having more than three electrodes; having more than one electrode connected to the same conductivity region
    • H03K17/735—Switching arrangements with several input- or output-terminals, e.g. multiplexers, distributors

Definitions

  • the present disclosure relates to a light source device and a measurement apparatus.
  • Japanese Unexamined Patent Application Publication No. 2019-57652 discloses a light-emitting component including a substrate, plural light-emitting elements, and plural thyristors.
  • the plural light-emitting elements are disposed on the substrate and emit light in a direction intersecting with a surface of the substrate.
  • the plural thyristors are stacked on the corresponding light-emitting elements and are turned ON to drive the corresponding light-emitting elements so that the light-emitting elements emit light or the amount of light emitted from the light-emitting elements is increased.
  • the plural thyristors each have a cavity in a path through which light emitted from a corresponding one of the light-emitting elements travels toward a corresponding one of the thyristors.
  • Japanese Unexamined Patent Application Publication No. 2021-158160 discloses a light-emitting device including a light source and a controller.
  • the light source includes plural light-emitting elements and plural drive elements.
  • the plural drive elements are disposed to correspond to the plural light-emitting elements. When the drive elements are turned ON, they drive the corresponding light-emitting elements to emit light.
  • the controller controls light emission of the plural light-emitting elements by switching between a sequential emission operation for causing the plural light-emitting elements to sequentially emit light and a simultaneous emission operation for causing the plural light-emitting elements to simultaneously emit light.
  • the light-emitting unit includes a light-emitting element provided with a capacitor such as a thyristor and turns ON the thyristor to cause the light-emitting element to emit light.
  • the thyristor has capacitance, and once it is turned ON, its ON state is maintained even without inputting a signal for turning ON the thyristor.
  • Non-limiting embodiments of the present disclosure relate to a light source device and a measurement apparatus which do not maintain the ON state when it is not necessary to maintain it.
  • aspects of certain non-limiting embodiments of the present disclosure overcome the above disadvantages and/or other disadvantages not described above.
  • aspects of the non-limiting embodiments are not required to overcome the disadvantages described above, and aspects of the non-limiting embodiments of the present disclosure may not overcome any of the disadvantages described above.
  • a light source device including: a light-emitting section including a light-emitting element, the light-emitting element including a thyristor; and a controller that performs control to supply a light-emitting current to the light-emitting section so as to cause the light-emitting element to emit light and then to supply a reemission stop pulse to the light-emitting section so as to cause the light-emitting element to become unable to reemit light.
  • FIG. 1 illustrates a light source device according to a first exemplary embodiment
  • FIG. 2 A is an equivalent circuit diagram for explaining the operation of a light-emitting unit by using a shift thyristor, a coupling transistor, and a set of a light-emission control thyristor and a vertical cavity surface emitting laser (VCSEL);
  • VCSEL vertical cavity surface emitting laser
  • FIG. 2 B is a partial sectional view illustrating the shift thyristor and the coupling transistor shown in FIG. 2 A ;
  • FIG. 3 A illustrates the layout of the light-emitting unit
  • FIG. 3 B is a sectional view taken along line IIIB-IIIB in FIG. 3 A ;
  • FIG. 4 is a timing chart illustrating the operation of the light source device according to the first exemplary embodiment
  • FIG. 5 is a timing chart illustrating the operation of a light source device different from the light source device shown in FIG. 4 ;
  • FIG. 6 A is a timing chart for explaining an intermittent light-emitting operation of a VCSEL
  • FIG. 6 B illustrates the voltage of a light-emission control thyristor and the light-emitting current of a VCSEL connected in series with each other when the light-emitting operation is performed in accordance with the timing chart of FIG. 6 A ;
  • FIG. 7 A is an equivalent circuit diagram of a light-emission control thyristor and a VCSEL;
  • FIG. 7 B illustrates semiconductor layers and parasitic capacitors generated at pn junctions of the light-emission control thyristor and the VCSEL;
  • FIG. 8 is a graph illustrating the voltage at the cathode of a light-emission control thyristor and the light-emitting current of a VCSEL in a case in which the OFF-resistance of a driver is varied;
  • FIG. 9 A is another graph illustrating the voltage at the cathode of the light-emission control thyristor and the light-emitting current of the VCSEL in a case in which the OFF-resistance of the driver is varied;
  • FIG. 9 B is an enlarged graph illustrating the voltage at the cathode of the light-emission control thyristor and a specific portion of the range of the light-emitting current of the VCSEL shown in FIG. 9 A ;
  • FIG. 10 illustrates a light source device according to a second exemplary embodiment
  • FIG. 11 illustrates a light source device according to a third exemplary embodiment
  • FIG. 12 is a timing chart for explaining a timing at which a reemission stop pulse is provided.
  • FIG. 13 is a block diagram illustrating the configuration of a measurement apparatus.
  • a light-emitting element is turned ON only when the ON state of a setter or the ON state of a thyristor provided for the light-emitting element is maintained. Maintaining the ON state of the setter and that of the thyristor may waste power which would not be consumed otherwise.
  • FIG. 1 illustrates a light source device 1 according to a first exemplary embodiment.
  • the right-side direction in the plane of the drawing is set to be a +x direction.
  • thyristors and transistors are represented by symbols, and resistors are indicated by rectangles.
  • Other drawings are also expressed in a similar manner.
  • the light source device 1 shown in FIG. 1 includes a light-emitting unit 10 and a controller 50 .
  • the light-emitting unit 10 includes a GND terminal, a VGK terminal, a ⁇ 1 terminal, a ⁇ 2 terminal, a VLD terminal, and a Vdrv terminal on one side ( ⁇ x direction).
  • GND represents a ground potential, which is a reference voltage.
  • the ground potential will be called the ground potential GND.
  • VGK represents a power supply potential (hereinafter called the power supply potential VGK).
  • VLD represents a light-emitting voltage (hereinafter called the light-emitting voltage VLD) used for supplying a light-emitting current.
  • Vdrv represents a driver voltage (hereinafter called the driver voltage Vdrv) which is output from a driver that turns ON/OFF the light-emitting current.
  • the light-emitting unit 10 includes a light-emitting section 11 and a shifter 12 .
  • the light-emitting section 11 includes multiple vertical cavity surface emitting lasers (VCSELs) and multiple light-emission control thyristors S.
  • VCSELs vertical cavity surface emitting lasers
  • FIG. 1 six VCSELs (VCSEL( 1 ) through VCSEL( 6 )) and six light-emission control thyristors S (light-emission control thyristors S( 1 ) through S( 6 )) are shown.
  • the VCSEL( 1 ) through VCSEL( 6 ) may collectively be called the VCSEL unless it is necessary to distinguish them from each other.
  • the light-emission control thyristors S( 1 ) through S( 6 ) may collectively be called the light-emission control thyristor S unless it is necessary to distinguish them from each other.
  • the anode of the VCSEL and the cathode of the light-emission control thyristor S are connected to each other. That is, the VCSEL and the light-emission control thyristor S denoted by the same number are connected in series with each other.
  • the six VCSELs and the six light-emission control thyristors S are arranged from one side ( ⁇ x direction) to the other side (+x direction) of the light-emitting unit 10 .
  • the series-connected VCSEL and light-emission control thyristor S is an example of a light-emitting element including a thyristor.
  • the light-emitting element may be an element including a thyristor whose pn junction emits light. Such an element is also an example of a light-emitting element including a thyristor.
  • the shifter 12 includes multiple shift thyristors T, coupling transistors Q, power supply line resistors Rg, current limiting resistors RL, and coupling resistors Rc.
  • FIG. 1 six shift thyristors T (shift thyristors T( 1 ) through T( 6 )) and six coupling transistors Q (coupling transistors Q( 1 ) through Q( 6 )) are shown.
  • the shift thyristors T( 1 ) through T( 6 ) may collectively be called the shift thyristor T unless it is necessary to distinguish them from each other.
  • the shifter 12 also includes six power supply line resistors Rg, six current limiting resistors RL, and six coupling resistors Rc, which are not denoted by numbers.
  • a shift thyristor T, a coupling transistor Q, a power supply line resistor Rg, a current limiting resistor RL, and a coupling resistor Rc form a shift unit 12 a .
  • Six shift units 12 a are arranged from one side ( ⁇ x direction) to the other side (+x direction) of the shifter 12 .
  • the shifter 12 includes a power supply line resistor Rg and a start resistor Rs at the end of one side ( ⁇ x direction).
  • the light-emitting unit 10 also includes current limiting resistors R 1 and R 2 .
  • the shift thyristor T and the coupling transistor Q are connected to each other.
  • the coupling transistor Q in the shift unit 12 a is connected to the light-emission control thyristor S of the light-emitting section 11 . That is, the light-emission control thyristors S( 1 ) through S( 6 ) and the coupling transistors Q( 1 ) through Q( 6 ) are respectively connected to each other.
  • the six shift thyristors T, six coupling transistors Q, and six pairs of light-emission control thyristors S and VCSELs are shown. However, the numbers of shift thyristors T, coupling transistors Q, and pairs of light-emission control thyristors S and VCSELs may be other than six.
  • the VGK terminal is connected to a power supply line 71
  • the GND terminal is connected to a ground line 73
  • the ⁇ 1 terminal is connected to a shift signal line 72 - 1
  • the ( 02 terminal is connected to a shift signal line 72 - 2
  • the VLD terminal is connected to a voltage supply line 74
  • the Vdrv terminal is connected to a driver voltage line 75 .
  • the shift signal lines 72 - 1 and 72 - 2 will be called the shift signal line 72 unless it is necessary to distinguish them from each other.
  • the controller 50 includes buffers Buf 1 and Buf 2 , power sources VS 1 and VS 2 , a driver Drv, and a light-emitting current limiting resistor RI.
  • the buffer Buf 1 supplies a shift signal p 1 to the ⁇ 1 terminal of the light-emitting unit 10 .
  • the buffer Buf 2 supplies a shift signal p 2 to the ⁇ 2 terminal of the light-emitting unit 10 .
  • the power source VS 1 generates a power supply potential VGK and supplies it to the VGK terminal of the light-emitting unit 10 .
  • the power source VS 1 also serves as a power source for the buffers Buf 1 and Buf 2 .
  • the buffers Buf 1 and Buf 2 substantially output a voltage of the power source VS 1 when the shift signals p 1 and p 2 are at a high (H) level, while they substantially output a voltage of the ground potential GND when the shift signals p 1 and p 2 are at a low (L) level.
  • a dedicated power source which is different from that generating the power supply potential VGK, may be used for the buffers Buf 1 and Buf 2 .
  • the power source VS 2 generates a light-emitting voltage VLD and supplies it to the VLD terminal of the light-emitting unit 10 .
  • the driver Drv uses an NMOS transistor, for example, as a driver element and is turned ON/OFF by a light-emitting signal p 1 applied to the gate of the NMOS transistor.
  • the source of the NMOS transistor is grounded, while the drain thereof is connected to the Vdrv terminal via the light-emitting current limiting resistor RI.
  • the driver Drv When the driver Drv is turned ON, it supplies the ground potential GND to the Vdrv terminal of the light-emitting unit 10 .
  • the driver Drv has a preset ON-resistance Ron and a preset OFF-resistance Roff, which will be discussed later.
  • the ON-resistance is the resistance when the driver Drv is ON, while the OFF-resistance is the resistance when the driver Drv is OFF.
  • the OFF-resistance may be formed by adjusting the structure of the NMOS transistor or by controlling the gate voltage of the NMOS transistor. Alternatively, the OFF-resistance may be formed by disposing a resistor in parallel with between the source and the drain of the NMOS transistor having a sufficiently high OFF resistance.
  • another element such as an insulated gate bipolar transistor (IGBT), may be used.
  • An NMOS transistor and an IGBT are examples of a driver element.
  • the relationship between the elements of the light-emitting unit 10 will be explained below by using the enlarged view of FIG. 2 A .
  • the light-emission control thyristor S, the shift thyristor T, and the coupling transistor Q may simply be called the light-emitting control thyristor, shift thyristor, and coupling transistor, respectively, without using the corresponding alphabetical characters.
  • the light-emission control thyristor S and the shift thyristor T may collectively be called the thyristor when it is not necessary to distinguish them from each other.
  • Each of the shift thyristor and the light-emission control thyristor is an npnp thyristor.
  • Each thyristor has an n-type cathode K (hereinafter simply called the cathode K), a p-type gate Gp (hereinafter simply called the p-gate Gp), an n-type gate Gn (hereinafter simply called the n-gate Gn), and a p-type anode A (hereinafter simply called the anode A).
  • the light-emission control thyristor S does not use the p-gate Gp for a control operation, and the p-gate Gp is not indicated in the drawings.
  • the coupling transistor is a multi-collector npn bipolar transistor.
  • the coupling transistor has an n-type emitter E (hereinafter simply called the emitter E), a p-type base B (hereinafter simply called the base B), and n-type collectors Cf and Cs (hereinafter simply called the collectors Cf and Cs).
  • the above-described alphabetical characters for the thyristor are used for all the thyristors, and the above-described alphabetical characters for the coupling transistor are used for all the coupling transistors.
  • Bipolar transistors forming a thyristor discussed below are also represented by these symbols.
  • the thyristor is constituted by a combination of a single-collector npn bipolar transistor and a single-collector pnp bipolar transistor, which will be discussed later, and is thus also represented by an emitter E, a base B, and a collector C.
  • the anode, cathode, n-gate, p-gate, emitter, base, and collector will be called the anode A, cathode K, n-gate Gn, p-gate Gp, emitter E, base B, and collector C, respectively, even when these alphabetical characters are not shown in the drawings.
  • the shift thyristor T, the coupling transistor Q, and a set of the light-emission control thyristor S and the VCSEL are formed by a III-V compound semiconductor, such as GaAs.
  • the forward voltage (diffusion potential) Vd at the junction of this compound semiconductor is set to be 1.5 V, while the saturation voltage Vc of a bipolar transistor formed by the compound semiconductor is set to be 0.3 V.
  • the ground potential GND is set to be 0 V, and the power supply potential VGK and the light-emitting voltage VLD are set to be 5 V.
  • the L level is 0 V (“L” (0 V)) and the H level is 5 V (“H” (5 V)).
  • the driver Drv is turned OFF.
  • the driver Drv is turned ON.
  • FIG. 2 A is an equivalent circuit diagram for explaining the operation of the light-emitting unit 10 by using the shift thyristor T( 1 ), the coupling transistor Q( 1 ), and a set of the light-emission control thyristor S( 1 ) and the VCSEL( 1 ).
  • FIG. 2 B is a sectional view illustrating the shift thyristor T( 1 ) and the coupling transistor Q( 1 ) shown in FIG. 2 A . In FIG. 2 A , the shift thyristor T( 2 ) is also shown.
  • the shift thyristor T( 1 ) is constituted by a combination of an npn bipolar transistor Tr 1 (hereinafter called the npn transistor Tr 1 ) and a pnp bipolar transistor Tr 2 (hereinafter called the pnp transistor Tr 2 ).
  • the base B of the npn transistor Tr 1 is connected to the collector C of the pnp transistor Tr 2 .
  • the collector C of the npn transistor Tr 1 is connected to the base B of the pnp transistor Tr 2 .
  • the emitter E of the npn transistor Tr 1 serves as the cathode K of the shift thyristor T( 1 ).
  • the collector C of the npn transistor Tr 1 (base B of the pnp transistor Tr 2 ) serves as the n-gate Gn of the shift thyristor T( 1 ).
  • the collector C of the pnp transistor Tr 2 (base B of the npn transistor Tr 1 ) serves as the p-gate Gp of the shift thyristor T( 1 ).
  • the emitter E of the pnp transistor Tr 2 serves as the anode A of the shift thyristor T( 1 ).
  • the emitter E of the npn transistor Tr 1 which serves as the cathode K of the shift thyristor T( 1 ), is connected to the ground line 73 connected to the GND terminal to which the ground potential GND is supplied.
  • the emitter E of the pnp transistor Tr 2 which serves as the anode A of the shift thyristor T( 1 ), is connected to the shift signal line 72 - 1 connected to the ⁇ 1 terminal.
  • the n-gate Gn is connected to a node between the start resistor Rs and the power supply line resistor Rg connected in series with each other.
  • the end of the start resistor Rs which is not the end connected to the power supply line resistor Rg, is connected to the shift signal line 72 - 2 connected to the ⁇ 2 terminal.
  • the end of the power supply line resistor Rg which is not the end connected to the start resistor Rs, is connected to the power supply line 71 connected to the VGK terminal to which the power supply potential VGK is supplied.
  • the shift signal p 1 is supplied to the ⁇ 1 terminal, while the shift signal p 2 is supplied to the ⁇ 2 terminal.
  • the base B is connected to the p-gate Gp of the shift thyristor T( 1 ) (the base B of the npn transistor Tr 1 and the collector C of the pnp transistor Tr 2 ), and the emitter E is connected to the ground line 73 .
  • the collector Cf is connected via the series-connected coupling resistor Rc and power supply line resistor Rg to the power supply line 71 to which the power supply potential VGK is supplied.
  • the node between the coupling resistor Rc and the power supply line resistor Rg is connected to the n-gate Gn of the shift thyristor T( 2 ).
  • the npn transistor Tr 1 of the shift thyristor T( 1 ) and the coupling transistor Q( 1 ) form a current mirror circuit. That is, a current proportional to a current flowing through the npn transistor Tr 1 flows through the coupling transistor Q( 1 ).
  • the collector Cs of the coupling transistor Q( 1 ) is connected to the n-gate Gn of the light-emission control thyristor S( 1 ) and is also connected via the current limiting resistor RL to the voltage supply line 74 connected to the VLD terminal to which the light-emitting voltage VLD is supplied.
  • the VCSEL( 1 ) and the light-emission control thyristor S( 1 ) are connected in series with each other. That is, the anode A of the VCSEL( 1 ) and the cathode K of the light-emission control thyristor S( 1 ) are connected to each other.
  • the anode A of the light-emission control thyristor S( 1 ) is connected to the voltage supply line 74 .
  • the cathode K of the VCSEL( 1 ) is connected to the driver voltage line 75 connected to the Vdrv terminal to which the driver voltage Vdrv is supplied.
  • the anode A of the shift thyristor T( 2 ) is connected to the shift signal line 72 - 2 connected to the ⁇ 2 terminal. As shown in FIG. 1 , the anodes A of the odd-numbered shift thyristors T are connected to the shift signal line 72 - 1 , while the anodes A of the even-numbered shift thyristors T are connected to the shift signal line 72 - 2 .
  • the connection relationship between the shift thyristor T( 2 ), coupling transistor Q( 2 ), light-emission control thyristor S( 2 ), and VCSEL( 2 ) through the connection relationship between the shift thyristor T( 6 ), coupling transistor Q( 6 ), light-emission control thyristor S( 6 ), and VCSEL( 6 ) are similar to that of the shift thyristor T( 1 ), coupling transistor Q( 1 ), light-emission control thyristor S( 1 ), and VCSEL( 1 ).
  • the shift signals p 1 and p 2 may also be indicated by the shift signals p 1 ( ⁇ 1 ) and p 2 ( ⁇ 2 ), respectively.
  • the power supply line 71 is set at the power supply potential VGK (5 V), and the ground line 73 is set at the ground potential GND (0 V).
  • the shift signals p 1 ( ⁇ 1 ) and p 2 ( ⁇ 2 ) are at “L” (0 V).
  • the npn transistor Tr 1 and the pnp transistor Tr 2 forming the shift thyristor T( 1 ) are in the OFF state.
  • the n-gate Gn of the shift thyristor T( 1 ) is connected to the node between the start resistor Rs and the power supply line resistor Rg connected in series with each other.
  • the end of the start resistor Rs which is not the end connected to the power supply line resistor Rg, is connected to the shift signal line 72 - 2 at “L” (0 V).
  • the end of the power supply line resistor Rg which is not the end connected to the start resistor Rs, is connected to the power supply line 71 at 5 V. Accordingly, the n-gate Gn is at the voltage obtained by distributing 5 V (voltage difference) between the start resistor Rs and the power supply line resistor Rg. If the voltage ratio between the start resistor Rs and the power supply line resistor Rg is 1:5, for example, the voltage at the n-gate Gn is 0.83 V.
  • the light-emitting signal pI is at “L” (0 V) and the driver Drv is OFF. Accordingly, the driver voltage Vdrv is not supplied to the driver voltage line 75 .
  • the above-described state is the initial state.
  • the voltage difference (4.7 V) between the emitter E (0 V) and the base B (4.7 V) of the npn transistor Tr 1 exceeds the forward voltage Vd (1.5 V).
  • the junction between the emitter E and the base B is thus forward-biased, and the npn transistor Tr 1 is shifted from the OFF state to the ON state.
  • both of the npn transistor Tr 1 and the pnp transistor Tr 2 of the shift thyristor T( 1 ) are turned ON, the shift thyristor T( 1 ) is shifted from the OFF state to the ON state.
  • “The shift thyristor T is shifted from the OFF state to the ON state” may also be called “the shift thyristor T is turned ON”.
  • “The shift thyristor T is shifted from the ON state to the OFF state” may also be called “the shift thyristor T is turned OFF”.
  • the shift thyristor T( 1 ) When the shift signal p 1 ( ⁇ 1 ) is shifted from “L” (0 V) to “H” (5 V) in the initial state, the shift thyristor T( 1 ) is turned ON and is shifted from the OFF state to the ON state.
  • the state in which the shift thyristor T can be turned ON when the anode A is made to have “H” (5 V) will be called “the shift thyristor T is in a state in which it can shift to the ON state”. This also applies to the other shift thyristors.
  • the voltage at the n-gate Gn of the shift thyristor T( 1 ) is changed to 0.3 V, which is the saturation voltage Vc.
  • the voltage at the anode A is determined by the total voltage of the forward voltage Vd and the saturation voltage Vc (Vd+Vc) and by a voltage drop due to the internal resistance of the shift thyristor T. In this example, the voltage at the anode A is assumed to be 1.9 V. That is, when the shift thyristor T( 1 ) is turned ON, the voltage of the shift signal line 72 - 1 is shifted from 5 V to 1.9 V. Then, the voltage at the p-gate Gp of the shift thyristor T( 1 ) is changed to 1.6 V.
  • the shift thyristor T( 1 ) is turned ON when the voltage at the n-gate Gn becomes lower than the voltage at the anode A by a value equal to the forward voltage Vd (1.5 V) or greater.
  • the shift thyristor T( 1 ) is turned OFF when the voltage of the shift signal line 72 - 1 (the voltage across the anode A and the cathode K) becomes lower than the above-described value, that is, 1.9 V.
  • the anode A is made to have “L” (0 V)
  • the voltage difference between the anode A and the cathode K is changed to 0 V, and the shift thyristor T( 1 ) is turned OFF.
  • the holding voltage Even with the application of the holding voltage, if a current for holding the ON state of the shift thyristor T( 1 ) is not supplied, the ON state of the shift thyristor T( 1 ) is not maintained. The current for holding the ON state will be called the holding current.
  • the npn transistor Tr 1 is also in the OFF state. Accordingly, the coupling transistor Q( 1 ) is also in the OFF state. At this time, the emitter E of the coupling transistor Q( 1 ) is set at the ground potential GND (0 V).
  • the voltage at the collector Cf becomes equal to the power supply potential VGK (5 V) via the series-connected power supply line resistor Rg and coupling resistor Rc.
  • the voltage at the collector Cs becomes equal to the light-emitting voltage VLD (5 V) via the current limiting resistor RL.
  • the shift thyristor T( 1 ) When the shift thyristor T( 1 ) is turned ON, that is, when the npn transistor Tr 1 enters the ON state, the p-gate Gp of the shift thyristor T( 1 ) is changed to 1.6 V, as discussed above. Since the base B of the coupling transistor Q( 1 ) is connected to the p-gate Gp of the shift thyristor T( 1 ), the voltage at the junction between the emitter E and the base B becomes greater than or equal to the forward voltage Vd (1.5 V). That is, the junction between the emitter E and the base B is forward-biased, and the coupling transistor Q( 1 ) is shifted from the OFF state to the ON state.
  • the voltage at the collector Cf becomes equal to the saturation voltage Vc (0.3 V).
  • the voltage at the collector Cs will be discussed later.
  • the voltage at the node between the power supply line resistor Rg and the coupling resistor Rc (n-gate Gn of the shift thyristor T( 2 )) is determined as follows.
  • the voltage difference between the voltage (5 V) of the power supply line 71 and the voltage (0.3 V) of the collector Cf is 4.7 V.
  • the voltage obtained by distributing 4.7 V between the power supply line resistor Rg and the coupling resistor Rc is the voltage at the node between the power supply line resistor Rg and the coupling resistor Rc.
  • the voltage ratio between the power supply line resistor Rg and the coupling resistor Rc is 5:1, for example, the voltage at the node between the power supply line resistor Rg and the coupling resistor Rc (n-gate Gn of the shift thyristor T( 2 )) is 1.08 V.
  • the anode A of the shift thyristor T( 2 ) is connected to the shift signal line 72 - 2 to which the shift signal p 2 ( ⁇ 2 ) is supplied. Since the shift signal p 2 ( ⁇ 2 ) is at “L” (0 V), the shift thyristor T( 2 ) is not turned ON. When the shift signal p 2 ( ⁇ 2 ) is changed from “L” (0 V) to “H” (5 V), the voltage at the anode A of the shift thyristor T( 2 ) is changed to “H” (5 V). The voltage difference (3.92 V) between the anode A and the n-gate Gn (1.08 V) becomes higher than the forward voltage Vd (1.5 V).
  • the junction between the n-gate Gn and the anode A is forward-biased, and the shift thyristor T( 2 ) is turned ON.
  • the shift thyristor T( 2 ) is turned ON.
  • multiple elements are provided and the element which is turned ON is sequentially shifted. This operation is called a shift operation.
  • elements to be turned ON or OFF are shift elements.
  • the collector Cs of the coupling transistor Q( 1 ) is connected to the n-gate Gn of the light-emission control thyristor S( 1 ).
  • the coupling transistor Q( 1 ) is turned ON, the pn junction between the anode A and the n-gate Gn of the light-emission control thyristor S( 1 ) is forward-biased.
  • the collector Cs of the coupling transistor Q( 1 ) draws a current from the light-emitting voltage VLD via the pn junction between the anode A and the n-gate Gn of the light-emission control thyristor S( 1 ), so that the voltage at the collector Cs results in substantially 3.5 V, which is obtained by subtracting the forward voltage Vd (1.5 V) from the light-emitting voltage VLD (5 V). Then, the driver Drv is turned ON, and when the driver voltage Vdrv is changed to the GND voltage (0 V), the cathode K of the VCSEL( 1 ) is changed to 0 V.
  • the voltage difference (5 V) between the light-emitting voltage VLD (5 V) and the driver voltage Vdrv (0 V) is thus applied to between the anode A of the light-emission control thyristor S( 1 ) and the cathode K of the VCSEL( 1 ).
  • This turns ON the light-emission control thyristor S( 1 ), causing a current to flow through the light-emission control thyristor S( 1 ) and the VCSEL( 1 ) connected in series with each other.
  • the VCSEL( 1 ) thus emits light.
  • the state in which the coupling transistor Q( 1 ) is turned ON and the n-gate Gn of the light-emission control thyristor S( 1 ) is at 3.5 V is a state in which the VCSEL( 1 ) emits light when the driver Drv is turned ON.
  • the state in which the coupling transistor Q( 1 ) is turned ON and the junction between the anode A and the n-gate Gn of the light-emission control thyristor S( 1 ) is forward-biased to 3.5 V will be called a state in which the VCSEL( 1 ) can emit light.
  • the light-emission control thyristor S controls the light emission of the VCSEL by using the potential of the n-gate Gn.
  • the power supply line 71 is at the power supply potential VGK (5 V)
  • the ground line 73 is at the ground potential GND (0 V)
  • the shift signals p 1 ( ⁇ 1 ) and p 2 ( ⁇ 2 ) are at “L” (0 V)
  • the driver Drv is OFF
  • the driver voltage Vdrv is not supplied to the driver voltage line 75 .
  • the shift thyristor T( 1 ) enters a state in which it can shift to the ON state.
  • the shift thyristor T( 2 ) When the coupling transistor Q( 1 ) is in the ON state, the shift thyristor T( 2 ) enters a state in which it can shift to the ON state.
  • the shift signal p 2 ( ⁇ 2 ) shift signal line 72 - 2 ) is changed from “L” (0 V) to “H” (5 V)
  • the shift thyristor T( 2 ) is turned ON.
  • the shift signal p 1 ( ⁇ 1 ) (shift signal line 72 - 1 ) is changed from “H” (5 V) to “L” (0 V)
  • the shift thyristor T( 1 ) is turned OFF since the cathode K and the anode A are made to have “L” (0 V).
  • the other shift thyristors T, coupling transistors Q, light-emission control thyristors S, and VCSELs are operated in a similar manner.
  • the light-emitting unit 10 is constituted by multiple semiconductor layers stacked on each other (see FIG. 3 B ).
  • FIG. 2 B illustrates multilayers forming part of the light-emitting unit 10 , that is, an n-type semiconductor layer 85 , a p-type semiconductor layer 86 , an n-type semiconductor layer 87 , and a p-type semiconductor layer 88 forming the shift thyristor T( 1 ) and the coupling transistor Q( 1 ).
  • the shift thyristor T( 1 ) uses the n-type semiconductor layer 85 as the cathode K, the p-type semiconductor layer 86 as the p-gate Gp, the n-type semiconductor layer 87 as the n-gate Gn, and the p-type semiconductor layer 88 as the anode A.
  • the coupling transistor Q( 1 ) uses the n-type semiconductor layer 85 as the emitter E, the p-type semiconductor layer 86 as the base B, and the n-type semiconductor layer 87 as the collectors Cf and Cs.
  • the cathode K of the shift thyristor T( 1 ) and the emitter E of the coupling transistor Q( 1 ) are electrically connected to each other via the n-type semiconductor layer 85 .
  • the p-gate Gp of the shift thyristor T( 1 ) and the base B of the coupling transistor Q( 1 ) are electrically connected to each other via the p-type semiconductor layer 86 .
  • the n-gate Gn of the shift thyristor T( 1 ) and the collectors Cf and Cs of the coupling transistor Q( 1 ) form the n-type semiconductor layer 87 , they are separated from each other.
  • the other shift thyristors T and coupling transistors Q are formed in a similar manner.
  • FIGS. 3 A and 3 B are respectively a plan view and a sectional view of the light-emitting unit 10 .
  • FIG. 3 A illustrates the layout of the light-emitting unit 10 .
  • FIG. 3 B is a sectional view taken along line IIIB-IIIB in FIG. 3 A .
  • the shift thyristors T( 1 ) through T( 4 ), coupling transistors Q( 1 ) through Q( 4 ), light-emission control thyristors S( 1 ) through S( 4 ), and VCSEL( 1 ) through VCSEL( 4 ) are mainly shown.
  • FIG. 3 A illustrates the layout of the light-emitting unit 10 .
  • FIG. 3 B is a sectional view taken along line IIIB-IIIB in FIG. 3 A .
  • the shift thyristors T( 1 ) through T( 4 ) the shift thyristors T( 1 ) through T( 4 ), coupling transistors Q( 1
  • the light-emitting unit 10 is constituted by an n-type semiconductor substrate 80 and multilayers stacked on the n-type semiconductor substrate 80 .
  • the multilayers are constituted by an n-type semiconductor layer 81 , an active layer 82 , a p-type semiconductor layer 83 , a tunnel junction layer 84 , an n-type semiconductor layer 85 , a p-type semiconductor layer 86 , an n-type semiconductor layer 87 , and a p-type semiconductor layer 88 .
  • Elements, such as the shift thyristor T, coupling transistor Q, light-emission control thyristor S, VCSEL, are constituted by plural islands, which are separated from each other by entirely or partially removing some semiconductor layers by etching.
  • An island may also be called a mesa.
  • Etching performed to form an island (mesa) may also be called mesa etching.
  • Islands (islands 300 and 301 through 307 ) will be explained by mainly referring to the island 301 including the light-emission control thyristor S( 1 ) and the VCSEL( 1 ) and the island 302 including the shift thyristor T( 1 ) and the coupling transistor Q( 1 ).
  • the island 300 is a region where the shifter 12 (see FIG. 1 ), such as the shift thyristor T( 1 ) and the coupling transistor Q( 1 ), is disposed.
  • the n-type semiconductor layer 81 , active layer 82 , p-type semiconductor layer 83 , tunnel junction layer 84 , and n-type semiconductor layer 85 entirely remain on the n-type semiconductor substrate 80 .
  • the VCSEL( 1 ) and the light-emission control thyristor S( 1 ) are stacked on each other.
  • the shift thyristor T( 1 ) and the coupling transistor Q( 1 ) shown in FIG. 2 B are disposed in the island 302 .
  • the current limiting resistor RL is disposed in the island 303 .
  • the power supply line resistor Rg and the coupling resistor Rc are disposed in the island 304 .
  • the power supply line resistor Rg and the start resistor Rs are disposed in the island 305 .
  • the current limiting resistor R 1 is disposed in the island 306 .
  • the current limiting resistor R 2 is disposed in the island 307 .
  • n-type semiconductor layer 81 , active layer 82 , p-type semiconductor layer 83 , tunnel junction layer 84 , and n-type semiconductor layer 85 , p-type semiconductor layer 86 , n-type semiconductor layer 87 , and p-type semiconductor layer 88 around the island 301 are removed by etching.
  • a p-ohmic electrode 321 which is likely to easily ohmic-contact a p-type semiconductor layer, is provided on the p-type semiconductor layer 88 .
  • An n-ohmic electrode 331 which is likely to easily ohmic-contact an n-type semiconductor layer, is provided on the n-type semiconductor layer 87 which is exposed by removing the p-type semiconductor layer 88 .
  • the VCSEL( 1 ) uses the n-type semiconductor layer 81 as the cathode K (see FIG. 2 A ), the active layer 82 as an active layer, the p-type semiconductor layer 83 as the anode A.
  • the light-emission control thyristor S( 1 ) uses the n-type semiconductor layer 85 as the cathode K, the p-type semiconductor layer 86 as the p-gate Gp (p-gate layer), the n-type semiconductor layer 87 as the n-gate Gn (n-gate layer), and the n-type semiconductor layer 88 as the anode A.
  • the n-ohmic electrode 331 is used as the n-gate Gn of the light-emission control thyristor S( 1 ).
  • the VCSEL( 1 ) is disposed on the n-type semiconductor substrate 80 , and the light-emission control thyristor S( 1 ) is disposed on the VCSEL( 1 ) with the tunnel junction layer 84 interposed therebetween.
  • the tunnel junction layer 84 is provided to make it difficult to cause a situation where a current does not flow between the p-type semiconductor layer 83 of the VCSEL( 1 ) and the n-type semiconductor layer 85 of the light-emission control thyristor S( 1 ) due to reverse biasing therebetween.
  • the tunnel junction layer 84 is a junction between an n ++ layer highly doped with an n-type impurity and a p ++ layer highly doped with a p-type impurity. A current flows through the tunnel junction layer 84 due to the tunnel effect even when the p-type semiconductor layer 83 and the n-type semiconductor layer 85 are reverse-biased.
  • the island 301 is formed cylindrically, except for a region where the n-ohmic electrode 331 is provided.
  • the p-ohmic electrode 321 which is formed in a ring-like shape, is disposed on the p-type semiconductor layer 88 of the cylindrical island 301 .
  • Part of the p-type semiconductor layer 83 which is exposed by etching, is oxidized from the peripheral portion of the cylindrical p-type semiconductor layer 83 and serves as a current blocking portion ⁇ .
  • the current blocking portion ⁇ is formed in a ring-like shape where a current is less likely to flow.
  • the center of the cylindrical p-type semiconductor layer 83 which is not oxidized, serves as a current passing portion ⁇ where a current is more likely to flow.
  • the current blocking portion ⁇ is formed in the following manner.
  • An AlAs layer or an AlGaAs layer having a high Al density is provided in the p-type semiconductor layer 83 .
  • the p-type semiconductor layer 83 is oxidized from the exposed peripheral portion, that is, Al is oxidized, thereby forming the current blocking portion ⁇ .
  • the peripheral portion of the VCSEL( 1 ) suffers from many defects due to etching and are thus likely to cause the occurrence of non-radiative recombination.
  • the provision of the current blocking portion ⁇ makes it less likely to consume power which would be used for non-radiative recombination, thereby enhancing power saving and light emission efficiency.
  • the light emission efficiency is represented by the amount of light that can be emitted per unit power.
  • the VCSEL( 1 ) emits light, which passes through the light-emission control thyristor S( 1 ) and is output.
  • the portion of the light-emission control thyristor S( 1 ) tunnel junction layer 84 and semiconductor layers 85 through 88 ) where light passes through may be removed.
  • the light-emission control thyristor S( 1 ) is formed in a doughnut shape. With this arrangement, light emitted from the VCSEL( 1 ) is less likely to be absorbed in the light-emission control thyristor S( 1 ) and the amount of light is less likely to be decreased.
  • a p-ohmic electrode 322 is provided on the p-type semiconductor layer 88 .
  • the p-ohmic electrode 322 is an electrode (anode A electrode) which is connected to the anode A of the shift thyristor T( 1 ) and which is connected to the shift signal line 72 - 1 to which the shift signal p 1 ( ⁇ 1 ) is supplied.
  • Three n-ohmic electrodes 332 , 333 , and 334 are provided on the n-type semiconductor layer 87 exposed by removing the p-type semiconductor layer 88 .
  • the n-ohmic electrode 332 is an electrode (collector Cs electrode) connected to the collector Cs of the coupling transistor Q( 1 ).
  • the n-ohmic electrode 334 is an electrode (collector Cf electrode) connected to the collector Cf of the coupling transistor Q( 1 ).
  • the n-type semiconductor layer 87 between the p-ohmic electrode 322 and the n-ohmic electrodes 332 and 334 is removed (see FIG. 2 B ).
  • the n-ohmic electrode 333 is an electrode (n-gate Gn electrode) connected to the n-gate Gn of the shift thyristor T( 1 ).
  • the p-type semiconductor layer 86 , n-type semiconductor layer 87 , and p-type semiconductor layer 88 around the island 303 are removed by etching.
  • two n-ohmic electrodes 335 and 336 are provided on the exposed n-type semiconductor layer 87 .
  • the n-type semiconductor layer 87 between the two n-ohmic electrodes 335 and 336 serves as the current limiting resistor RL.
  • the island 304 is formed similarly to the island 303 .
  • Three n-ohmic electrodes 337 , 338 , and 339 are provided on the n-type semiconductor layer 87 exposed by removing the p-type semiconductor layer 88 .
  • the n-type semiconductor layer 87 between the n-ohmic electrodes 337 and 338 serves as the coupling resistor Rc, while the n-type semiconductor layer 87 between the n-ohmic electrodes 338 and 339 serves as the power supply line resistor Rg.
  • the island 305 is formed similarly to the island 304 .
  • the start resistor Rs and the power supply line resistor Rg are disposed in the island 305 .
  • the islands 306 and 307 are formed similarly to the island 303 .
  • the current limiting resistors R 1 and R 2 are respectively disposed in the islands 306 and 307 .
  • An n-ohmic electrode 340 is provided on the exposed n-type semiconductor layer 85 in the island 300 .
  • a back-side electrode 79 is provided on the back side of the n-type semiconductor substrate 80 .
  • lines (power supply line 71 , shift signal lines 72 - 1 and 72 - 2 , and voltage supply line 74 ) used for connecting elements in the light-emitting unit 10 are indicated by the thick straight lines.
  • the p-ohmic electrode 321 in the island 301 which is the anode A electrode of the light-emission control thyristor S( 1 ), is connected to the voltage supply line 74 to which the light-emitting voltage VLD is supplied.
  • the n-ohmic electrode 331 in the island 301 which is the n-gate Gn of the light-emission control thyristor S( 1 ) is connected to the n-ohmic electrode 332 in the island 302 , which is the collector Cs electrode of the coupling transistor Q( 1 ).
  • the n-ohmic electrode 332 is connected to the n-ohmic electrode 336 corresponding to the current limiting resistor RL in the island 303 .
  • the n-ohmic electrode 335 in the island 303 is connected to the voltage supply line 74 .
  • the p-ohmic electrode 322 in the island 302 which is the anode A electrode of the shift thyristor T( 1 ), is connected to the shift signal line 72 - 1 .
  • the shift signal line 72 - 1 is connected, via the current limiting resistor R 1 in the island 306 , to the ⁇ 1 terminal to which the shift signal p 1 is supplied.
  • the n-ohmic electrode 333 in the island 302 which is the n-gate Gn electrode of the shift thyristor T( 1 ), is connected to an n-ohmic electrode, which is a node between the power supply line resistor Rg and the start resistor Rs, in the island 305 .
  • the n-ohmic electrode 334 in the island 302 which is the collector Cf electrode of the coupling transistor Q( 1 ), is connected to the n-ohmic electrode 337 in the island 304 , which is one of the n-ohmic electrodes corresponding to the coupling resistor Rc.
  • the n-ohmic electrode 338 in the island 304 which is the other one of the n-ohmic electrodes corresponding to the coupling resistor Rc, is connected to an n-ohmic electrode, which is the n-gate Gn electrode of the shift thyristor T( 2 ).
  • the n-ohmic electrode 339 in the island 304 which is the other one of the n-ohmic electrodes corresponding to the power supply line resistor Rg, is connected to the power supply line 71 to which the power supply potential VGK is supplied.
  • One of the n-ohmic electrodes corresponding to the start resistor Rs in the island 305 is connected to the shift signal line 72 - 2 .
  • the other one of the n-ohmic electrodes corresponding to the power supply line resistor Rg in the island 305 is connected to the power supply line 71 .
  • the shift signal line 72 - 2 is connected, via the current limiting resistor R 2 in the island 307 , to the ⁇ 2 terminal to which the shift signal p 2 is supplied.
  • the shift signal line 72 - 1 is connected to the p-ohmic electrodes, which are the anode A electrodes of the odd-numbered shift thyristors T.
  • the shift signal line 72 - 2 is connected to the p-ohmic electrodes, which are the anode A electrodes of the even-numbered shift thyristors T.
  • the other shift thyristors T, coupling transistors Q, light-emission control thyristors S, and VCSELs are formed similarly to the shift thyristor T( 1 ), coupling transistor Q( 1 ), light-emission control thyristor S( 1 ), and VCSEL( 1 ), respectively.
  • the n-ohmic electrode 340 disposed on the exposed n-type semiconductor layer 85 in the island 300 serves as the GND terminal to which the ground potential GND is supplied.
  • the back-side electrode 79 on the back side of the n-type semiconductor substrate 80 is the Vdrv terminal to which the driver voltage Vdrv is supplied.
  • the shift thyristor T and the coupling transistor Q are disposed on the multilayer semiconductor layer (structure) equivalent to that on which the light-emission control thyristor S and the VCSEL are disposed.
  • the n-ohmic electrode 340 is disposed on the n-type semiconductor layer 85 and is set to the ground potential GND.
  • the driver voltage Vdrv ( ⁇ 0 V) is supplied to the back-side electrode 79 on the back side of the n-type semiconductor substrate 80 .
  • the potential of the anode A of the p-type semiconductor layer 83 is bound to be lower than that of the cathode K of the n-type semiconductor layer 81 , and the pn junction formed by the n-type semiconductor layer 81 , active layer 82 , and p-type semiconductor layer 83 is not forward-biased.
  • the n-type semiconductor layer 85 in the island 300 is insulated from the back-side electrode 79 .
  • the light-emitting unit 10 is disposed on the semiconductor substrate 80 constituted by one semiconductor.
  • FIG. 4 is a timing chart illustrating the operation of the light source device 1 according to the first exemplary embodiment.
  • the horizontal axis indicates the time, and the time elapses from time a to time r in alphabetical order.
  • a temporal change in each of the shift signals p 1 and p 2 and the light-emitting signal pI is shown, and the shift thyristor T, the light-emission control thyristor S, and the VCSEL which are turned ON are each indicated by its alphabetical character and number.
  • a set of the light-emission control thyristor S and the VCSEL is represented by S/VCSEL.
  • the VCSEL( 1 ) and VCSEL( 6 ) are caused to emit light.
  • the light-emitting unit 10 After the light-emitting unit 10 has caused the VCSEL( 1 ) to emit light from the initial state, it returns to the initial state and then causes the VCSEL( 6 ) to emit light. In this manner, the light-emitting unit 10 causes the VCSEL( 1 ) and the VCSEL( 6 ) to emit light.
  • a desirable VCSEL can be selected and be caused to emit light. In other words, VCSELs can randomly emit light.
  • the VCSEL( 1 ) emits light as a result of the shift thyristor T( 1 ) being turned ON, while the VCSEL( 6 ) emits light as a result of the shift thyristor T( 6 ) being turned ON.
  • the VCSEL( 1 ) and VCSEL( 6 ) are each caused to intermittently emit light multiple times (five times in FIG. 4 ). If the VCSEL is caused to emit light in this manner, the light-emission control thyristor S is more likely to be maintained in a state in which the VCSEL can emit light. Once the shift thyristor T causes the light-emission control thyristor S to be in such a state, the VCSEL is more likely to reemit light regardless of whether the shift thyristor T is ON.
  • the timing chart of FIG. 4 will be explained below by referring to FIG. 1 .
  • the initial state is a state in which the power supply line 71 is at the power supply potential VGK (5 V), the ground line 73 is at the ground potential GND (0 V), the shift signals p 1 ( ⁇ 1 ) and p 2 ( ⁇ 2 ) are at “L” (0 V), the driver Drv is OFF, and the driver voltage Vdrv is not supplied to the driver voltage line 75 .
  • the shift thyristor T( 1 ) is in a state in which it can shift to the ON state.
  • the shift signal p 1 is changed from “L” (0 V) to “H” (5 V). Then, the shift thyristor T( 1 ) is turned ON and shifts from the OFF state to the ON state. Then, the anode A and the n-gate Gn of the light-emission control thyristor S( 1 ) is forward-biased and the VCSEL( 1 ) enters a state in which it can emit light.
  • the light-emitting signal pI is changed from “L” (0 V) to “H” (5 V).
  • the driver Drv is changed from OFF to ON and the driver voltage Vdrv is changed to the ground potential GND (0 V).
  • the light-emission control thyristor S( 1 ) is turned ON and the light-emitting voltage VLD (5 V) is applied to between the anode A of the light-emission control thyristor S( 1 ) and the cathode K of the VCSEL( 1 ).
  • a current flows through the light-emission control thyristor S( 1 ) and the VCSEL( 1 ) connected in series with each other, thereby causing the VCSEL( 1 ) to emit light.
  • the shift signal p 1 is changed from “H” (5 V) to “L” (0 V). Then, the shift thyristor T( 1 ) is turned OFF and shifts from the ON state to the OFF state.
  • the light-emitting signal pI is changed from “H” (5 V) to “L” (0 V). Then, a current stops flowing through the anode A of the light-emission control thyristor S( 1 ) and the cathode K of the VCSEL( 1 ), thereby causing the VCSEL( 1 ) to stop emitting light.
  • the light-emitting signal pI is switched from “L” (0 V) to “H” (5 V) and from “H” (5 V) to “L” (0 V) four times, thereby causing the VCSEL( 1 ) to emit light four times.
  • the VCSEL intermittently emits light and are thus called light-emitting pulses.
  • the period from time b to time c is a pulse width, while the interval between light-emitting pulses (interval from time s to time tin FIG. 6 A , which will be discussed later) is a pulse interval.
  • the shift signal p 1 ( ⁇ 1 ) is at “L” (0 V)
  • the shift thyristor T( 1 ) is OFF, and no current flows through the shift thyristor T( 1 ).
  • the states of the other shift thyristors T are similar to that of the shift thyristor T( 1 ). Power is thus less likely to be consumed in the shifter 12 (see FIG. 1 ).
  • the initial state is resumed.
  • the shift thyristor T( 1 ) is in a state in which it can shift to the ON state.
  • the shift signal p 1 is changed from “L” (0 V) to “H” (5 V). Then, as in time a, the shift thyristor T( 1 ) is turned ON and shifts from the OFF state to the ON state.
  • the shift signal p 2 is changed from “L” (0 V) to “H” (5 V). Then, the shift thyristor T( 2 ) is turned ON and shifts from the OFF state to the ON state.
  • the shift signal p 1 is changed from “H” (5 V) to “L” (0 V). Then, the shift thyristor T( 1 ) is turned OFF.
  • the shift thyristor T( 3 ) is turned ON, and, at time i, the shift thyristor T( 2 ) is turned OFF.
  • the shift thyristor T( 4 ) is turned ON, and, at time k, the shift thyristor T( 3 ) is turned OFF.
  • the shift thyristor T( 5 ) is turned ON, and, at time m, the shift thyristor T( 4 ) is turned OFF.
  • the shift thyristor T( 6 ) is turned ON, and, at time o, the shift thyristor T( 5 ) is turned OFF.
  • the anode A and the n-gate Gn of the light-emission control thyristor S( 6 ) is forward-biased, and the VCSEL( 6 ) enters a state in which it can emit light.
  • the light-emitting signal pI is changed from “L” (0 V) to “H” (5 V).
  • the driver Drv is changed from OFF to ON and the driver voltage Vdrv is changed to the ground potential GND (0 V).
  • the VCSEL( 6 ) emits light, as the VCSEL( 1 ) emits light in time b.
  • the shift signal p 2 is changed from “H” (5 V) to “L” (0 V). Then, the shift thyristor T( 6 ) is turned OFF.
  • the light-emitting signal pI is changed from “H” (5 V) to “L” (0 V). Then, the VCSEL( 6 ) stops emitting light.
  • the light-emitting signal pI is switched from “L” (0 V) to “H” (5 V) and from “H” (5 V) to “L” (0 V) four times, thereby causing the VCSEL( 6 ) to emit light four times.
  • the shift signal p 2 ( ⁇ 2 ) is at “L” (0 V)
  • the shift thyristor T( 6 ) is OFF, and no current flows through the shift thyristor T( 6 ).
  • the states of the other shift thyristors T are similar to that of the shift thyristor T( 6 ). Power is thus less likely to be consumed in the shifter 12 (see FIG. 1 ).
  • the shifter 12 turns ON the shift thyristor T on the upstream side in the shifting direction and then turns ON the shift thyristor T on the downstream side in the shifting direction. Then, the shifter 12 turns OFF the shift thyristor T on the upstream side.
  • the ON state is sequentially shifted among the shift thyristors T in the shifter 12 , that is, the above-described shift operation is performed.
  • the shift operation based on the shift signals p 1 and p 2 there is a period (from time f to time g, for example) for which two adjacent shift thyristors T are ON at the same time.
  • FIG. 5 is a timing chart illustrating the operation of a light source device different from the light source device 1 .
  • the timing chart in FIG. 5 is assumed to represent the operation of the related art.
  • the same light-emitting unit 10 of the first exemplary embodiment is used.
  • the horizontal axis indicates the time, as in FIG. 4 .
  • the ON state of the shift thyristor T( 1 ) is maintained during the period from time c to time d for which the light emission of the VCSEL( 1 ) is intermittently repeated.
  • the ON state of the shift thyristor T( 6 ) is maintained during the period from time q to time r for which the light emission of the VCSEL( 6 ) is intermittently repeated.
  • a current for maintaining the ON state continues to flow through the shift thyristor T( 1 ) or T( 6 ).
  • the shift thyristor T( 1 ) is maintained in the ON state.
  • the anode A and the n-gate Gn of the light-emission thyristor S( 1 ) is forward-biased, and the VCSEL( 1 ) is maintained in state in which it can emit light.
  • the VCSEL is caused to intermittently emit light during a period for which the shift thyristor T is in the OFF state (period from time c to time d in FIG. 4 , for example). This will be explained below.
  • FIG. 6 A is a timing chart, which is part of the timing chart starting from time a in FIG. 4 .
  • FIG. 6 B illustrates the voltage of the light-emission control thyristor S( 1 ) and the light-emitting current of the VCSEL( 1 ).
  • the light-emission control thyristor S( 1 ) and the VCSEL( 1 ) are connected in series with each other.
  • time s to time y are added to the period from time c to time d (see FIG. 4 ) in alphabetical order.
  • the horizontal axis indicates the time (ns).
  • the left vertical axis indicates the voltages (V) at the p-gate Gp, n-gate Gn, and cathode K of the light-emission control thyristor S( 1 ).
  • the right vertical axis indicates the light-emitting current (mA) of the VCSEL( 1 ).
  • the shift signal p 1 is changed from “L” (0 V) to “H” (5 V) and the shift thyristor T( 1 ) is turned ON.
  • the light-emitting signal pI is changed from “L” (0 V) to “H” (5 V) and the VCSEL( 1 ) starts to emit light.
  • time b corresponds to 100 ns on the time axis in FIG. 6 B .
  • the shift signal p 1 is changed from “H” (5 V) to “L” (0 V) and the shift thyristor T( 1 ) is turned OFF.
  • the light-emitting signal pI is changed from “H” (5 V) to “L” (0 V) and the VCSEL( 1 ) stops emitting light.
  • the VCSEL( 1 ) is OFF for 100 ns from time s.
  • the light-emitting signal pI is changed from “L” (0 V) to “H” (5 V) again and the VCSEL( 1 ) starts to reemit light.
  • the switching of the light-emitting signal pI between “H” (5 V) and “L” (0 V) as in the period from time b to time t is repeated.
  • the VCSEL( 1 ) emits light for 20 ns from time b, which corresponds to 100 ns, and then stops emitting light for 100 ns, and then reemits light for 20 ns. In this manner, the VCSEL( 1 ) repeatedly reemits light at the equal time intervals. In the above-described light-emitting operation, even when the shift signal p 1 is changed from “H” (5 V) to “L” (0 V) to turn OFF the shift thyristor T( 1 ), the VCSEL( 1 ) emits light because the light-emitting signal pI is still ON.
  • the VCSEL( 6 ) When causing the VCSEL( 6 ) to emit light after the VCSEL( 1 ), if the time interval between the VCSEL( 1 ) and the VCSEL( 6 ) is too short, not only the VCSEL( 6 ), but also the VCSEL( 1 ) emits light erroneously. More specifically, if the time interval is as short as that from time s to time t, when the shift thyristor T( 6 ) sets the VCSEL( 6 ) as the next VCSEL to emit light, the VCSEL( 1 ) also emits light, as well as the VCSEL( 6 ).
  • FIG. 6 B illustrates simulation results obtained under the conditions that the voltages and resistance of elements shown in FIG. 1 are as follows: the light-emitting current limiting resistor RI is 100 ⁇ , the power supply potential VGK supplied from the power source VS 1 and the light-emitting voltage VLD supplied from the power source VS 2 are 5 V, the ON-resistance Ron of the driver Drv is 1 ⁇ , and the OFF-resistance Roff of the driver Drv is 1 M ⁇ .
  • the p-gate Gp is not used, the voltage thereof is shown in FIG. 6 B .
  • FIG. 7 A is an equivalent circuit diagram of the light-emission control thyristor S( 1 ) and the VCSEL( 1 ).
  • FIG. 7 B illustrates semiconductor layers (see FIG. 3 B ) and parasitic capacitors generated at pn junctions.
  • the n-type semiconductor layer 81 forming the cathode K of the VCSEL( 1 ) and the p-type semiconductor layer 83 forming the anode A of the VCSEL( 1 ) are shown.
  • FIG. 7 B illustrates semiconductor layers (see FIG. 3 B ) and parasitic capacitors generated at pn junctions.
  • the n-type semiconductor layer 81 forming the cathode K of the VCSEL( 1 ) and the p-type semiconductor layer 83 forming the anode A of the VCSEL( 1 ) are shown.
  • the n-type semiconductor layer 85 forming the cathode K of the light-emission control thyristor S( 1 ), the p-type semiconductor layer 86 forming the p-gate Gp of the light-emission control thyristor S( 1 ), the n-type semiconductor layer 87 forming the n-gate Gn of the light-emission control thyristor S( 1 ), and the p-type semiconductor layer 88 forming the anode A of the light-emission control thyristor S( 1 ) are shown.
  • the active layer 82 and the tunnel junction layer 84 are not shown.
  • a parasitic capacitor Cv is generated at the pn junction between the cathode K (n-type semiconductor layer 81 ) and the anode A (p-type semiconductor layer 83 ) of the VCSEL( 1 ).
  • a parasitic capacitor Cgk is generated at the pn junction between the cathode K (n-type semiconductor layer 85 ) and the p-gate Gp (p-type semiconductor layer 86 ) of the light-emission control thyristor S( 1 ).
  • a parasitic capacitor Cgg is generated at the pn junction between the p-gate Gp (p-type semiconductor layer 86 ) and the n-gate Gn (n-type semiconductor layer 87 ) of the light-emission control thyristor S( 1 ).
  • a parasitic capacitor Cag is generated at the pn junction between the n-gate Gn (n-type semiconductor layer 87 ) and the anode A (p-type semiconductor layer 88 ) of the light-emission control thyristor S( 1 ).
  • the tunnel junction layer 84 is interposed between the anode A (p-type semiconductor layer 83 ) of the VCSEL( 1 ) and the cathode K (n-type semiconductor layer 85 ) of the light-emission control thyristor S( 1 ).
  • the anode A of the VCSEL( 1 ) and the cathode K of the light-emission control thyristor S( 1 ) are at the same potential and no parasitic capacitor is generated therebetween.
  • FIG. 6 A The timing chart of FIG. 6 A will be explained by referring to FIGS. 7 A and 7 B .
  • the anode A and the n-gate Gn of the light-emitting control thyristor S( 1 ) is forward-biased, and the voltage at the n-gate Gn results in 3.5 V, which is obtained by subtracting the forward voltage Vd (1.5 V) from the voltage at the anode A.
  • the voltage at the p-gate Gp results in 4.7 V, which is obtained by subtracting the saturation voltage Vc (0.3 V) from the voltage at the anode A.
  • the voltage at the cathode K results in 1.7 V, which is lower than the voltage at the p-gate Gp by 2 ⁇ Vd, by reflecting the forward voltage Vd (1.5 V). This is the state immediately before time b in FIG. 6 A , which corresponds to 100 ns on the time axis in FIG. 6 B .
  • the light-emitting signal pI is changed from “L” (0 V) to “H” (5 V) and the driver Drv is turned ON.
  • the driver voltage line 75 connected to the cathode K of the VCSEL( 1 ) is changed to the ground potential GND via the driver Drv and the light-emitting current limiting resistor RI. This turns ON the light-emission control thyristor S( 1 ) and causes the VCSEL( 1 ) to emit light.
  • the n-gate Gn is at a voltage of about 3.2 V
  • the p-gate Gp is at a voltage of about 4.7 V
  • the cathode K is at a voltage of about 1.7 V.
  • the shift signal p 1 is changed from “H” (5 V) to “L” (0 V).
  • the voltage at the n-gate Gn still remains the same since the VCSEL( 1 ) keeps emitting light.
  • the light-emitting signal pI is changed from “H” (5 V) to “L” (0 V) and the driver Drv is turned OFF.
  • the voltage of the driver Drv is switched from the ON-resistance Ron at 1 ⁇ to the OFF-resistance Roff at 1 M ⁇ .
  • Roff With a sufficiently high OFF-resistance Roff, the current between the anode A of the light-emission control thyristor S( 1 ) and the cathode K of the VCSEL( 1 ) becomes lower than the holding current.
  • the light-emission control thyristor S( 1 ) is thus turned OFF and is shifted from the ON state to the OFF state, and the VCSEL( 1 ) stops emitting light.
  • the voltage at the n-gate Gn rises toward the light-emitting voltage VLD (5 V) since the n-gate Gn is connected to the voltage supply line 74 at the light-emitting voltage VLD (5 V) via the current limiting resistor RL. That is, the parasitic capacitor Cag (capacitance value Cag) is discharged at a time constant of RL ⁇ Cag via the current limiting resistor RL (resistance value RL). Meanwhile, electric charge stored in the parasitic capacitors Cgg, Cgk, and Cv is unable to move, and the voltage at the p-gate Gp and that at the cathode K are thus raised by a value corresponding to a rise in the voltage at the n-gate Gn.
  • the voltage at the n-gate Gn is about 5 V
  • the voltage at the p-gate Gp is about 6 V
  • the voltage at the cathode K is about 3 V.
  • the light-emitting signal pI is changed from “L” (0 V) to “H” (5 V) and the driver Drv is turned ON again.
  • the driver voltage line 75 connected to the cathode K of the VCSEL( 1 ) suddenly starts to shift toward the ground potential GND (0 V).
  • a displacement current thus flows through the parasitic capacitors Cag, Cgg, and Cgk, and, by using this displacement current as a threshold current, the light-emission control thyristor S( 1 ) is turned ON and the VCSEL( 1 ) emits light.
  • the light-emitting signal pI is changed from “H” (5 V) to “L” (0 V) and the driver Drv is turned OFF. Then, the light-emission control thyristor S( 1 ) is turned OFF and the VCSEL( 1 ) stops emitting light, as at time s. As a result of repeating the operation performed from time s to time t, the VCSEL( 1 ) intermittently emits light multiple times.
  • FIG. 8 is a graph illustrating the voltage at the cathode K of the light-emission control thyristor S( 1 ) and the light-emitting current of the VCSEL( 1 ) in a case in which the OFF-resistance of the driver Drv is varied.
  • FIG. 8 shows simulation results obtained under the conditions that the OFF-resistance is set to 50 k ⁇ , 100 k ⁇ , 200 k ⁇ , 500 k ⁇ , and 1 M ⁇ . The timing chart in FIG. 6 A is used for this simulation.
  • the OFF-resistance Roff As the OFF-resistance Roff is lower, a voltage drop at the cathode K of the light-emission control thyristor S( 1 ) after the VCSEL( 1 ) stops emitting light is greater.
  • the OFF-resistance Roff is set to any of 100 k ⁇ , 200 k ⁇ , 500 k ⁇ , and 1 M ⁇
  • the VCSEL( 1 ) reemits light at time t after the light-emission control thyristor S( 1 ) is turned OFF, that is, the shifter 12 is turned OFF, at the timing in FIG. 6 A . That is, even after the shifter 12 is turned OFF, the VCSEL( 1 ) can intermittently emit light multiple times (VCSEL( 1 ) becomes able to reemit light).
  • the VCSEL( 1 ) does not reemit light at time t after the light-emission control thyristor S( 1 ) is turned OFF, that is, the shifter 12 is turned OFF, at the timing in FIG. 6 A .
  • the reason for this is as follows. Even though the driver Drv is turned ON, a voltage change of the driver voltage line 75 connected to the cathode K of the VCSEL( 1 ) is small and a sufficiently high displacement current does not flow, thereby failing to turn ON the light-emission control thyristor S( 1 ).
  • the simulations show that the voltage at the cathode K which makes the light-emission control thyristor S( 1 ) no longer turned ON is lower than 0.9 V. At this voltage of the cathode K, the light-emission control thyristor S( 1 ) is no longer turned ON and the VCSEL( 1 ) no longer reemits light (VCSEL( 1 ) becomes unable to reemit light).
  • the voltage at the cathode K is determined by the parasitic capacitor at each pn junction (parasitic capacitors Cgg, Cgk, and Cv in FIG.
  • the light-emission control thyristor S is an example of a capacitor, and a set of the light-emission control thyristor S and the VCSEL connected in series with each other is an example of a light-emitting element having a capacitor.
  • the OFF-resistance Roff of the driver Drv may desirably be higher to cause the VCSEL to intermittently emit light after the shifter 12 is turned OFF.
  • the VCSEL is turned ON, it becomes unable to reemit light if the voltage at the cathode K of the light-emission control thyristor S becomes lower than 0.9 V.
  • a voltage drop at the cathode K of the light-emission control thyristor S becomes smaller as the OFF-resistance Roff is higher.
  • FIG. 9 A is another graph illustrating the voltage at the cathode K of the light-emission control thyristor S( 1 ) and the light-emitting current of the VCSEL( 1 ) in a case in which the OFF-resistance of the driver Drv is varied.
  • the right vertical axis indicates the entire range of the light-emitting current.
  • the right vertical axis indicates a specific portion of the range of the light-emitting current in FIG. 9 A .
  • FIGS. 9 A and 9 B the simulation results obtained when the OFF-resistance Roff is set to be 50 k ⁇ and 30 k ⁇ are shown.
  • the timing chart in FIG. 6 A is used for this simulation.
  • the result obtained when the OFF-resistance Roff is 50 k ⁇ is the same as that shown in FIG. 8 .
  • the OFF-resistance Roff is low, when the driver Drv is turned OFF, the voltage at the cathode K of the light-emission control thyristor S approaches 0 V very quickly. If the OFF-resistance Roff is very low, however, a current higher than or equal to the holding current continues to flow through the light-emitting control thyristor S even after the driver Drv is turned OFF, and the light-emission control thyristor S is not turned OFF.
  • FIG. 9 A when the OFF-resistance Roff is 50 k ⁇ , the VCSEL does not reemit light at time t. On the other hand, however, when the OFF-resistance Roff is 30 k ⁇ , the VCSEL reemits light at time t. At time v and time x, the VCSEL also reemits light.
  • the enlarged graph in FIG. 9 B shows that, when the OFF-resistance Roff is 50 k ⁇ , the light-emitting current falls during the period for which the driver Drv is OFF and is reduced to almost 0 A at time u onwards.
  • FIG. 9 B shows that, when the OFF-resistance Roff is 50 k ⁇ , the light-emitting current falls during the period for which the driver Drv is OFF and is reduced to almost 0 A at time u onwards.
  • the OFF-resistance Roff of the driver Drv is set in accordance with a preset period before the VCSEL becomes unable to reemit light (that is, the OFF period for another VCSEL).
  • the driver Drv has only one OFF-resistance Roff.
  • the OFF-resistance Roff of the driver Drv can be switched between multiple values.
  • FIG. 10 illustrates a light source device 2 according to the second exemplary embodiment.
  • the controller 50 of the light source device 2 includes two drivers Drv 1 and Drv 2 instead of the driver Drv used in the first exemplary embodiment.
  • the driver Drv 1 has an ON-resistance Ron 1 and an OFF-resistance Roff 1 .
  • the driver Drv 2 has an ON-resistance Ron 2 and an OFF-resistance Roff 2 .
  • the ON-resistance Ron 1 and the ON-resistance Ron 2 may be the same or may be different from each other.
  • the OFF-resistance Roff 1 and the OFF-resistance Roff 2 are different (Roff 1 >Roff 2 , for example).
  • the drivers Drv 1 and Drv 2 are connected to the light-emitting current limiting resistor RI via a switch SW. As a result of changing the state of the switch SW, the drivers Drv 1 and Drv 2 can be switched therebetween.
  • the switch SW may be an NMOS transistor having a larger resistance value than one of the OFF-resistance Roff 1 and the OFF-resistance Roff 2 .
  • the driver Drv 2 having a smaller OFF-resistance Roff 2 can drop the voltage at the cathode K of the light-emission control thyristor S faster than the driver Drv 1 having a larger OFF-resistance Roff 1 .
  • the period for which the VCSEL intermittently emits light may be set by switching between the drivers Drv 1 and Drv 2 .
  • the above-described OFF period may also be set by switching between the drivers Drv 1 and Drv 2 .
  • the value of the OFF-resistance Roff may be changed in the following manner.
  • Plural resistors having different resistance values may be connected via a switch in parallel to between the source and the drain of an NMOS transistor, which is used as a driver Drv, having a sufficiently high OFF resistance. By switching the state of the switch, the OFF-resistance Roff of the driver Drv can be changed.
  • the period before the VCSEL becomes unable to reemit light is determined by the OFF-resistance Roff of the driver Drv.
  • a reemission stop pulse is provided to cause the VCSEL to stop reemitting light.
  • the light-emission control thyristor S may be likely to remain its ON state and the VCSEL may be kept ON, or the VCSEL may enter a state in which it can emit light due to malfunctioning of the light-emission control thyristor S.
  • the reemission stop pulse can help the VCSEL stop emitting light. Without the reemission stop pulse, to stop a VCSEL from reemitting light, it is necessary to wait until electric charge of the light-emission control thyristor S connected to this VCSEL is discharged.
  • FIG. 11 illustrates a light source device 3 according to the third exemplary embodiment.
  • the controller 50 of the light source device 3 includes a driver Drv 3 and a reemission stop current limiting resistor RJ, in addition to the elements provided in the controller 50 of the light source device 1 shown in FIG. 1 .
  • the driver Dr 3 uses an NMOS transistor, for example, as a driver element and is turned ON/OFF by a reemission stop signal pJ applied to the gate of the NMOS transistor.
  • the source of the NMOS transistor used as the driver Drv 3 is grounded, and the drain thereof is connected to the Vdrv terminal via the reemission stop current limiting resistor RJ.
  • the reemission stop signal pJ is a signal having a ground potential GND (“L” (0 V)) and a power supply potential VGK (“H” (5 V)). It is also assumed that the driver Drv 3 is turned OFF when the reemission stop signal pJ is at “L” (0 V) and is turned ON when the reemission stop signal pJ is at “H” (5 V). That is, the period for which the reemission stop signal pJ is at “H” (5 V) corresponds to the width of the reemission stop pulse.
  • the driver Drv is an example of a first driver, while the driver Drv 3 is an example of a second driver.
  • the ON-resistance Ron of the driver Drv 3 is close to 0 ⁇ , and the OFF-resistance Roff thereof is close to ⁇ (infinite).
  • the reemission stop current limiting resistor RJ reduces the voltage at the cathode K of the light-emission control thyristor S for a preset reemission stop period (corresponding to the width of the reemission stop pulse) to a value which makes the VCSEL unable to reemit light.
  • the reemission stop current limiting resistor RJ reduces the value of the voltage at the cathode K to the value when the OFF-resistance Roff is 50 k ⁇ shown in FIG. 8 .
  • the resistance value of the reemission stop current limiting resistor RJ is set to be a value at which a current higher than or equal to the holding current does not flow through the light-emission control thyristor S.
  • FIG. 12 is a timing chart for explaining a timing at which a reemission stop pulse is provided.
  • the time period from time n to time r of the timing chart in FIG. 4 is mainly extracted and a reemission stop pulse is provided during this time period.
  • Time aa and time ab are added to the time period between time o and time p in FIG. 12 .
  • the reemission stop pulse be provided after the time at which a series of light emission operations of a VCSEL is completed (time din FIG. 4 ) and before the time at which the next VCSEL starts emitting light (time p in FIG. 4 ).
  • the VCSEL( 6 ) is caused to emit light as the next VCSEL.
  • the shift signal p 2 is changed from “L” (0 V) to “H” (5 V), and the shift thyristor T( 6 ) is turned ON and is shifted from the OFF state to the ON state.
  • the shift signal p 1 is changed from “H” (5 V) to “L” (0 V), and the shift thyristor T( 5 ) is turned OFF and is shifted from the ON state to the OFF state.
  • Time aa is a timing at which no elements other than the shift thyristor T( 6 ) for setting the VCSEL( 6 ) to emit light is in the ON state.
  • the reemission stop signal pJ is changed from “H” (5 V) to “L” (0 V) and the driver Drv 3 is turned OFF.
  • the light-emitting signal pI is changed from “L” (0 V) to “H” (5 V) to cause the VCSEL( 6 ) to emit light.
  • the period from time aa to time ab for which the reemission stop signal pJ is at “H” (5 V) corresponds to the pulse width of a reemission stop pulse.
  • the VCSEL( 6 ) is caused to emit light in this example, another VCSEL may be caused to emit light.
  • the reason for this is as follows. While the shifter 12 is shifting the ON state, the voltage at the n-gate Gn of the light-emission control thyristor S corresponding to a VCSEL other than the VCSEL to emit light is reduced, and the voltage at the n-gate Gn of the light-emission control thyristor S is fluctuated due to noise during the shift operation.
  • the reemission stop pulse can reset (initialize) the influence of such a voltage drop and a voltage fluctuation. In this manner, the reemission stop pulse contributes to, not only making the previous VCSEL unable to reemit light, but also making any VCSEL in the light-emitting unit 10 unable to emit light. Hence, the reemission stop pulse may be inserted before the first VCSEL is caused to emit light.
  • the reemission stop current limiting resistor RJ may be provided as follows. Plural resistors having different resistance values may be connected in parallel to between the source and the drain of the NMOS transistor having a sufficiently high OFF resistance, and one of the resistors may be used as the reemission stop current limiting resistor RJ. The plural resistors may be connected to between the source and the drain of the NMOS transistor via a switch and a reemission stop pulse may be generated by changing the state of the switch.
  • the width of the reemission stop pulse is set to be narrower than that of the light-emitting pulse, and/or the current value of the reemission stop pulse is set to be smaller than that of the light-emitting pulse. This makes it possible for the reemission stop pulse to stop the VCSEL from emitting light more reliably.
  • a pulse having a low velocity dV/dt of a voltage change may desirably be supplied to the driver voltage line 75 .
  • the light-emitting voltage VLD is applied to the n-gate Gn of the light-emission control thyristor S via the current limiting resistor RL. Accordingly, electric charge in the n-gate layer 87 , which is the n-gate Gn, is more likely to be removed (see FIG.
  • the threshold voltage of the light-emission control thyristor S is varied in accordance with the amount of remaining electric charge. Because of the above-described reason, a pulse having a low velocity dV/dt of a voltage change may be supplied to the driver voltage line 75 so as to raise the threshold voltage of the light-emission control thyristor S, thereby making it difficult for the light-emission control thyristor S to be turned ON.
  • the VCSEL every time the light-emitting signal pI is set at “H” (5 V), the VCSEL is caused to emit light.
  • the VCSEL may not necessarily fully emit light when the light-emission control thyristor S is turned ON and instead be set in a state in which the amount of light is reduced. That is, this period is provided not to cause the VCSEL to fully emit light, but to extend the period for which the VCSEL is ready to reemit light.
  • the voltage at the cathode K rises to reset the period for which the VCSEL is ready to reemit light.
  • a pulse having a narrower pulse width than that of the light-emitting pulse may be used, and/or the current to flow through the VCSEL may be set to be lower than that for causing the VCSEL to emit light. This can reduce the amount of light of the VCSEL instead of causing the VCSEL to fully emit light when the light-emission control thyristor S is turned ON.
  • the period for which the VCSEL is ready to reemit light restarts. It is thus possible to extend the period for which the VCSEL is ready to reemit light to a desirable period.
  • the light-emitting unit 10 includes plural light-emitting elements.
  • the exemplary embodiments may be applicable to a light-emitting unit including only one light-emitting element.
  • the light-emitting element is unlikely to emit light.
  • the VCSEL when the VCSEL is in a state in which it can emit light because of the state of the light-emission control thyristor S, it may emit light.
  • the VCSEL is not in a state in which it can emit light because of the state of the light-emission control thyristor S, it is unlikely to emit light.
  • the light-emitting elements emit light multiple times.
  • the exemplary embodiments may be applicable to a light source device which allows light-emitting elements to emit light only one time. As shown in FIGS. 6 A and 6 B , even after the light-emitting element (VCSEL in the exemplary embodiments) emits light for the first time, it can keep reemitting light. Depending on the configuration of the light-emitting unit, once the light-emitting element emits light, it may be able to reemit light for as long as milliseconds.
  • the light-emitting element is set to emit light only one time, the interval between a period for which one light-emitting element emits light and another period for which another light-emitting element emits light is decreased. With this arrangement, a light-emitting element is less likely to emit light erroneously.
  • the cathode common configuration is employed in the above-described light-emitting unit 10
  • the anode common configuration may be utilized.
  • p-ohmic electrodes instead of providing n-ohmic electrodes on an n-gate layer (n-type semiconductor layer 87 ), p-ohmic electrodes may be provided on a p-gate layer (p-type semiconductor layer 86 ).
  • a coupling transistor Q is used to connect shift thyristors T.
  • a diode or a resistor may be used to connect shift thyristors T.
  • the shifter 12 is used as a setter by way of example.
  • the setter may be configured to cause a driver to directly transmit a signal to the thyristor of a light-emitting element.
  • the light source devices 1 , 2 , and 3 of the first, second, and third embodiments may be applicable to a measurement apparatus that measures a three-dimensional configuration (hereinafter called a 3D configuration) of a subject to be measured.
  • the measurement apparatus is an apparatus that measures a 3D configuration based on a time-of-flight (ToF) method using the time-of-flight of light.
  • the measurement apparatus includes a light source device and a three-dimensional sensor (hereinafter called a 3D sensor).
  • the ToF method the time from when light is emitted from the light source device until when the 3D sensor receives light reflected by a subject is measured, and based on the measured time, the distance to the subject is calculated.
  • the 3D configuration of the subject is specified in this manner. Measuring a 3D configuration may also be called three-dimensional measurement, 3D measurement, and 3D sensing.
  • the 3D sensor is an example of a light receiver.
  • the measurement apparatus may be used for recognizing a subject from its specified 3D configuration.
  • the measurement apparatus may be installed in a mobile information processing terminal and be used for recognizing the face of a user who has accessed the mobile information processing terminal. That is, the measurement apparatus obtains the 3D configuration of the face of a user having accessed the mobile information processing terminal, determines whether the user is authorized to access the terminal, and permits the user to use the terminal only when the user is an authorized user.
  • the measurement apparatus may also be used for continuously measuring the 3D configuration of a subject, such as in augmented reality (AR).
  • AR augmented reality
  • the measurement apparatus may also be applied to an information processing apparatus, such as a personal computer (PC), other than a mobile information processing terminal.
  • an information processing apparatus such as a personal computer (PC)
  • PC personal computer
  • FIG. 13 is a block diagram illustrating the configuration of a measurement apparatus 100 .
  • the measurement apparatus 100 includes a 3D sensor 5 and the light source device 1 , 2 , or 3 provided with the light-emitting unit 10 and the controller 50 .
  • the light source device 1 , 2 , or 3 emits light toward a subject.
  • the 3D sensor 5 receives light (reflected light) reflected by and returned from the subject.
  • the 3D sensor 5 outputs information on the distance to the subject (distance information), which is measured by the ToF method based on the time from when light is emitted until when the reflected light is returned.
  • the measurement apparatus 100 may include a measurement controller 200 .
  • the measurement controller 200 is constituted by a computer including a central processing unit (CPU), a read only memory (ROM), and a random access memory (RAM), for example.
  • the measurement controller 200 specifies the 3D configuration of a subject, based on the distance information obtained from the 3D sensor 5 .
  • the present disclosure may also be implemented as follows.
  • a shifter is constituted by transfer elements through which the ON state is transferred in order of the arrangement of the transfer elements. This configuration may make it easier to form the shifter than in the configuration in which the ON state is not transferred.
  • a light-emitting element In a light-emitting unit, as a result of a thyristor of a shifter entering the ON state, a light-emitting element is changed to a state in which it can emit light due to a thyristor function. This may make it possible to separately control the shifter and control the light-emitting unit.
  • a light-emitting element is constituted by a surface emitting element and a thyristor connected in series with each other. This may make it easy to enhance the light-emission characteristics.

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  • Condensed Matter Physics & Semiconductors (AREA)
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